This invention relates to a pumping system of the type employing a main pump and a high pressure centrifugal pump both of which are driven by an engine through a suitable drive means. In some applications, such as a pumping system used for firefighting applications, it is necessary to engage and disengage the high pressure pump from the engine drive so that all the horsepower of the engine can be delivered to the main pump. In the prior art systems, mechanical clutches are employed to engage and disengage the high pressure pump from the engine drive. However, mechanical clutches are a problem because of their relatively high failure rate which usually is caused by the system operators slipping of the clutch during the engagement of the high pressure pump. Slipping of the clutch causes the clutch facings to burn out. Also, the initial cost and replacement of the mechanical clutches involves a substantial cost.
It is the general object of the invention to provide in the pumping system of the indicated type comprising means for disengaging the high pressure centrifugal pump in a manner that is reliable and avoids the failure problems of mechanical clutches.
Another object of the invention is to provide a means for disengaging the high pressure pump by a simple manual movement of the operator so that the operator can perform the function of pump disengagement by a simple and foolproof maneuver.
Briefly stated, the general object of the invention is achieved by providing what may be termed an "air clutch" means whereby air is selectively introduced into the inlet of the high pressure centrifugal pump to cause air binding of the pump impellers, i.e., the replacement of the incompressible fluid (water) with the compressible fluid (air) at the inlet region of the impellers to prevent the build-up of pump pressure thereby rendering said pump incapable of pumping any fluid. This action, in effect, de-clutches the high pressure pump by a simple hydraulic action. Accordingly, de-clutching of the high pressure pump reduces the horsepower drag on the drive means for the main pump to a minimum so that all the engine horsepower can be directed to the main pump.
It will be apparent that the "air clutch" arrangement of the invention is very reliable and it is not subject to abuse by the operator. There are no parts that can wear out. Furthermore, the simple hydraulic system of the invention is less expensive to manufacture and maintain than a mechanical clutch system.
For example, the amount of power reduced can be seen from a typical fire pump's operating condition wherein the main pump is running at 500 GPM and a pressure of 450 psi. The unloading of the high pressure pump at this condition, by putting it in a non-pumping mode by means of the "air clutch" of the invention, will reduce the power comsumption at this particular condition from 260 to 225 horsepower.
In accordance with another feature of the invention, means are provided for cooling and lubricating the outboard sleeve bearing of the high pressure pump and the mechanical seal on the inboard side of the impeller for the high pressure pump. It is noted that even though no hydraulic work is being done by the high pressure pump impellers when they are in the non-pumping mode thereof, the pump impellers and the pump shaft are still turning whereby it is necessary to prevent damage to the seal and bearings as discussed above.